Lecture 24 - Community Ecology 16 - Biodiversity Drivers 03 - 11/17/2025

Last lecture class before the exam on Wednesday.
Reminder of class on Friday with a final problem set due before Thanksgiving.
Content from today’s class will be included in the exam: students should study this along with previously discussed material.

Focus on the concept of disturbance and its impact on biodiversity at local scales.
Discussion of the trade-offs in biodiversity drivers related to colonization and competition.
- Colonization-Competition Trade-off:
- This concept ties with ecological succession, where colonizers and competing species interact over time.
Consideration of whether biodiversity affects the stability of a system as explored in the assigned paper.

Define disturbance within ecological contexts and discuss its implications for stability and biodiversity.
Recap previous discussions on biodiversity at local scales, particularly regarding productivity.
Introduce the concept of ecological succession as an important biological process.

Disturbance: An event that disrupts an ecosystem or community, affecting the availability of resources and species.
Different types of disturbances can include:
- Fire: Acts as a disturbance, with frequency and intensity as important measures.
- Natural Disasters: Such as floods or storms that can reset ecological processes.
Intermediate Disturbance Hypothesis: Intermediate levels of disturbance can enhance biodiversity, creating conditions optimal for coexistence.

Ecological Succession: The process by which ecosystems change and develop over time following a disturbance.
- Major phases include:
- Pioneers: First species to colonize disturbed areas (e.g., pioneer species).
- Intermediate Species: Colonizers that arrive as conditions become more favorable.
- Climax Community: A stable, mature community that undergoes little change over time.
Both land and aquatic systems undergo succession; the principles apply to ecosystems as a whole.

Colonization-Competition Trade-off: A concept where those species that are excellent colonizers may not be as effective competitors.
- Example: Pioneer species colonize rapidly in disturbed areas but might not be efficient in utilizing resources compared to later successional species.
Life history traits influence these trade-offs, emphasizing variation in reproductive strategies and survival.
Life History Traits: Traits tied to reproduction and survival rates that affect species success in various habitats:
- R-strategists: Species that maximize reproduction (e.g., mice).
- K-strategists: Species that maximize survival and resource allocation (e.g., elephants).

Case studies including multivariate analysis of colonization in disturbed ecosystems reveal patterns supporting the intermediate disturbance hypothesis
- Graphs showing changes in biodiversity across four phases of colonization illustrate species richness in relation to disturbance intensity.
- Empirical data confirms humped relationship between productivity and species diversity: too much or too little productivity can decrease biodiversity.

Investigated the effect of disturbance on ant species colonization across trees with different damage levels.
- Demonstrated variation depending on ant species’ competitive abilities and their responses to disturbance.

Resilience: The ability of an ecosystem to restore itself after a disturbance.
Resistance: The capacity of an ecosystem to withstand disturbances without changing.
Studies examined biomass and species richness before disturbances, finding:
- Higher species richness correlates with greater resistance and resilience.
- However, at high levels of diversity, the relationship becomes less clear, supporting a nuanced view of diversity and stability dynamics.

Ending with the understanding that disturbance impacts biodiversity and stability differently depending on ecological context.
Encouragement to consider the nuances of local versus global biodiversity dynamics and the implications for conservation strategies before the exam.